The background of aspects of the present disclosure is hereinafter introduced with the discussion of techniques relating to its context. However, even when this discussion refers to documents, acts, artifacts and the like, it does not suggest or represent that the discussed techniques are part of the prior art or are common general knowledge in the field relevant to the present disclosure.
One or more aspects of the present disclosure relate to the field of electronics. More specifically, one or more aspects relate to circuitized structures.
Circuitized structures (i.e., insulating substrates supporting electric circuits) are commonly used in several applications. A typical example is a Printed Circuit Board (PCB), which comprises a laminate of glass fiber, (thermosetting) resin and metal (with one or more layers of metal that are suitably patterned to define the desired electric circuit). The PCB is generally used to mount electronic devices (wherein the insulating substrate supports the electronic devices and the electric circuit interconnects them). Moreover, a particular type of circuitized structure is an Insulated Metal Substrate (IMS), which further comprises a dissipation plate of metal that is laminated with the insulating substrate. The dissipation plate is thicker than the insulating substrate, which in turn is thicker than the electric circuit. The IMS is generally used to mount electronic devices of power type (with the dissipation plate that facilitates the dissipation of heat that is produced by the electronic devices in operation).
The above-mentioned circuitized structures are rigid, with a substantially bi-dimensional, or flat, configuration. Therefore, they are unsuitable to make circuitized structures with a 3-Dimensional (3-D) configuration. Indeed, any attempt to bend these (rigid) circuitized structures is very likely to damage them. This is especially true for the IMSs, because of their highly asymmetrical construction. Particularly, during any bending the inner part and the outer part of any rigid circuitized structure are subject to compressive deformations and to tensile deformations, respectively. This may cause cracks in the outer part of the insulating substrate (because of the relatively low resistance to tensile stresses of most of the resins). Moreover, in the inner part of the insulating substrate this may cause cracks as well (if the resin is relatively hard) or wrinkles (if the resin is relatively soft). The insulating substrate may also transmit strains to the electric circuit; these strains (in addition to the ones already caused by the bending) may compromise the integrity of the electric circuit. In addition, during the bending the insulating substrate stretches and slides with respect to the dissipation plate and to the electric circuit. This may cause a delamination of the circuitized structure, since adhesion between the insulating substrate and the dissipation plate/electric circuit is mostly given by mechanical intimacy between the resin and the roughness (peaks and valleys) of the corresponding metal. All of the above may create opens in the electric circuit and/or paths for short circuits (to the dissipation plate).
Another example of a circuitized structure is a Flexible Printed Circuit (FPC), wherein the insulating substrate is made of a flexible material (for example, polyimide). The FPC allows the circuitized structure to conform to specific shapes or to bend during its use. However, the FPCs may be unsuitable to support the weight of the electronic devices mounted thereon and/or to protect them efficiently from a mechanical point of view.
Therefore, a stiffener (for example, a metal sheet) may be attached to the FPC (on the opposite side of its electric circuit) to make it more rigid. Rigid-flex printed circuits are also available, wherein a rigid metal substrate is laminated with the (flexible) insulating substrate. However, the above-mentioned circuitized structures require manufacturing processes that are not standard, and thus, relatively expensive. This limits their use only to special products for low volume applications.